The popularization of crowd computing leads to an increase in information processing configurations using an application on a server of a data center by a TCP/IP (transmission control protocol/Internet protocol) communication through a network such as a WAN (wide area network). The WAN has a variety of configurations, but taking use of the WAN in an enterprise work into consideration, there are used a VPN (virtual private network) and a high-quality network that ensure a bandwidth of a private line, and support switching to another route with a high speed at the time of failure.
For example, in a private line service using an MPLS-TP (multi-protocol label switching transport profile) or a ring protocol, primary and backup end-to-end communication paths are configured for service users in advance, and the primary path is normally used. When the network failure occurs, the primary communication path is switched to the backup communication path at a high speed such as about 50 ms, thereby making it possible to minimize a down time of the network.
However, even if the above high-quality network is used, an application of the user is delayed by 50 ms or more which is caused by switching the communication path when the network failure occurs, resulting in the deterioration of a response such that the operation is stopped, or a screen display speed is decreased. This derives from a fact that a large amount of data packets and ACK (acknowledge) packets for responses are lost when the network failure occurs, and communication processing is again repeated after the time-out has been elapsed in a TCP layer of a TCP/IP communication. A time-out period is, for example, about 3 seconds.
Japanese Unexamined Patent Application Publication No. 2003-158558, which is the background art of this technical field, discloses, as a purpose, “there are provided a packet communication method and a proposal node, which can rapidly restart a communication after the interception of continuous packet loss caused by communication interception has been recovered, and are simple in the configuration and low in the costs.”
Also, Japanese Unexamined Patent Application Publication No. 2003-158558 discloses, as its solution, “The recovery of a communication after the communication interception is detected by a communication interception recovery detector 27, and pseudo redundant acknowledgement is transmitted from an ACK transmitter 25 by the optimum number of times calculated by a computing unit 28. At the same time, an advertisement receiving window size is normally under-advertised, and the size is increased and advertised at the time of recovery.”
Also, Japanese Unexamined Patent Application Publication No. 2008-17417 discloses, as a purpose, “There is provided a packet communication apparatus with a simple configuration which does not generate unnecessary traffic within the network.”
Japanese Unexamined Patent Application Publication No. 2008-17417 discloses, as its solution, “A transmission period of an ARP packet is set to a first period (period of existence confirmation) to wait for an ARP transmission timing (Step S2). The ARP packet is transmitted at the transmission timing (Step 3). Thereafter, if an ARP response is present, the control flow is shifted to Step S7 whereas if the ARP response is absent, the control flow proceeds to Step S5 (Step S4). The transmission or reception of data is stopped in Step S5, the transmission period is set to a second period (period of recovery detection) (Step S6), and the control flow returns to Step S2. If the transmission or reception of data is not being stopped in Step S7, the control flow is returned to Step S2, and if the transmission or reception of data is being stopped, the control flow proceeds to Step S8. The data transmission and reception stop processing is canceled, and the transmission period is returned to the first period in Step S8, and the control flow is returned to Step S2 (Step S9).”